A woman was killed and 11 other people, including seven children, were injured in a series of hit-and-run accidents through busy suburban streets in Cardiff yesterday.

Police arrested a man on suspicion of murder and seized a white van following half an hour of chaos at school pick-up time on Friday.

Witnesses described how mothers and children were knocked over and others leapt to safety. One woman was said to have been dragged underneath the van. The ambulance service described injuries suffered by some survivors as "serious".

Superintendent Julian Williams, of South Wales police, said a 31-year-old man was being held on suspicion of murder. Williams said: "Whether the actions were deliberate or reckless is a matter for the inquiry and the person will obviously be spoken to."

Police were not naming the 32-year-old woman who died, but she was identified locally as mother-of-three Karina Menzies. She is believed to have been walking with her children when she was hit.

Williams said it was too early to say what part the police pursuit of the vehicle played and could not confirm whether pedestrians had been deliberately targeted. "It is a complicated series of incidents which we are trying to piece together. It is a tragic event," Williams said.

The incident is believed to have begun at about 3.30pm near the City of Cardiff Stadium in Leckwith, to the west of the city centre. Witnesses claimed there was a violent row and a white van drove off at speed, hitting a woman as it left the scene. It is believed the van headed further west towards the suburb of Ely.

Police confirmed the fatal collision happened at Cowbridge Road West, outside the fire station. Witnesses said the driver appeared to veer towards the building.

Firefighters on duty dashed out to help the woman and others who had been hit. The fire station forecourt was sealed off and forensic experts were working at the scene on Friday night.

The 31-year-old man was arrested near the Merrie Harrier pub in Llandough, to the south west of the city centre, and was being held at Cardiff Bay police station. Officers were examining a white Iveco van.

Witnesses described their shock at the chain of events. Shopkeeper Phil Jones said: "It was absolutely incredible – right outside my shop the van aimed straight at a mother and two children walking on the pavement and mowed them down. He then drove straight across the road and smashed into a man and woman with their baby in a pushchair. He just smashed into them before heading away.

"In about 100 yards, he veered off the road and hit another two boys and a mother and a boy on a bike. People were rushing out of houses trying to help the injured and covering them with blankets until the ambulances arrived. The baby was covered in blood; people were lying on pavements moaning."

Natalie Howell, 28, said people tried to block the van to stop it driving off after one accident. "But he went up on the pavement and sped off," she said.

Tony McGuinness, 48, said: "We saw a young woman being resuscitated at the roadside – it didn't look too good for her. There were police everywhere, a helicopter up above and ambulances were going past every minute."

Harbhajan Dhaliwal, 42, who runs a convenience store,said: "People are very upset and panicked by what has happened. I had one woman come in who said her niece has been injured. She is really upset and worried and was going to go to the hospital."

Among the victims were Annie Lewis, 22, her two-year-old daughter Amelia-May, who was in a pram, and her partner Adam Lewis. Amelia-May was left covered in blood from facial injuries and Annie, a student, suffered a broken leg.

Adam's grandmother, Maureen Lewis, 80, said: "It was total mayhem out there – the driver of the white van was driving fast and furious at anyone in his path."

Ely resident Gail Harford, 40, said: "The driver was not just running over people but reversing over them, too. It's too horrendous for words."